The investigation of intumescent flame-retarded polypropylene using poly(hexamethylene terephthalamide) as carbonization agent

A novel intumescent flame retardant, containing ammonium polyphosphate (APP), and poly(hexamethylene terephthalamide) (PA6T), was prepared for flame retarding polypropylene (PP). The flame retardation of the PP composites was characterized by limiting oxygen index (LOI). The thermal degradation of the composites was investigated by means of thermogravimetric analysis (TG) and TG coupled with Fourier transform infrared spectroscopy (TG-FTIR). The morphology of the char obtained after combustion of the composites was studied by scanning electron microscopy. It has been found the intumescent flame retardant showed good flame retardancy, with the LOI value of the PA6T/APP/PP (5/25/70) system increasing from 17.5 to 32. Meanwhile, the TG and TG-FTIR work indicated that PA6T could be effective as a carbonization agent and there was a synergistic reaction between PA6T and APP, which effectively promoted the char formation of the PP composites. Moreover, it was revealed that uniform and compact intumescent char layer was formed after combustion of the intumescent flame retarded PP composites.     

聚乙炔热氧化过程的研究

本文测定了聚乙炔在氮气、空气和氧气中的等速升温热重曲线,测定了不同聚乙炔样品热氧化的恒温热重曲线,比较了聚合体系和顺反结构等对热氧化行为的影响。观察到钕催化聚乙炔的热氧化诱导现象。动力学分析表明,氧化反应对聚乙炔和氧气浓度都接近表观一级反应,顺式聚乙炔的表观活化能为42±6ki/mol,反式聚乙炔为51±6kJ/mol。用红外光谱跟踪氧化过程,表明含氧基团可分两类,分属于中间和最终产物,由此推断了可能的氧化反应。     

A novel technique for the interfacial characterisation of glass fibre–polypropylene systems

In the present work, a new technique was developed to determine the interfacial properties of two opaque glass fibre/polypropylene (GF/PP) systems via fragmentation tests on single filament model composites. Fragmentation tests usually require the fibre inside the composites to be completely aligned in the loading direction. Since PP matrices are non-transparent, it is not possible to guarantee a priori this condition. Hence, a novel technique was developed to determine the inclination of the filaments embedded in the composites. The fibre–polymer systems were also evaluated by comparing their interfacial properties with the overall mechanical properties determined on pultruded GF/PP composites. The present work shows that the knowledge of the interfacial properties is important, not only to compare alternative fibre/matrix systems, but also to assess whether the level of adhesion in these systems is adequate to fabricate composites with good mechanical properties.     

表面复合纳米SiO_2和碳纳米管玻璃纤维增强尼龙6的结构与性能

利用静电相互作用在玻璃纤维(GF)表面分别复合纳米二氧化硅(SiO2)和多壁碳纳米管(MWNTs),制备了GF-SiO2、GF-MWNTs复合增强体,并通过转矩流变仪制备了尼龙6(PA6)/GF-SiO2和尼龙6(PA6)/GF-MWNTs复合材料.利用扫描电子显微镜(SEM),示差扫描量热仪(DSC),热机械分析仪(DMA)等手段研究了复合材料的微观结构、热学及力学性能.结果表明,静电复合的方法可以使纳米二氧化硅(nano-SiO2)、多壁碳纳米管(MWNTs)在GF表面达到均匀吸附,复合增强体能加快尼龙6的结晶速度,并使材料的玻璃化温度、动态模量、拉伸强度、结晶温度等明显提高,其中GF-MWNTs对复合材料性能的提高最明显,拉伸强度提升了21%,模量提高了28%.     

Application of cooling curve analysis in solidification pattern and structure control of grey cast irons

In this article, the composites based on long glass fibre reinforced polypropylene/intumescent flame retardant (LGFPP/IFR) were prepared by melt blending. The influence of thermal oxidative ageing on the LGFPP/IFR composites with different thermal oxidative ageing time at 140 °C was studied by means of oven heating. The thermal stability and flammability of the composites were respectively investigated by thermal gravimetric analysis (TG), limiting oxygen index (LOI), UL-94 test, cone calorimeter test (CCT), scanning electronic microscopy (SEM), mechanical properties test and energy-dispersive X-ray analysis (EDAX). A trend of increase first and then decrease in LOI values was shown in 0–50 days ageing, with the same trend as thermal stability obtained from TG in nitrogen condition. The CCT results indicated that the LGFPP/IFR composites after ageing achieved a higher heat release rate, which means a higher fire risk. The mechanical properties showed a global decrease in just 10 days ageing. Morphologies obtained from SEM showed that both the rupture of PP matrix and fibre interface debonding led to the decrease in mechanical properties. The EDAX proved that IFR particles could emerge and gather on the surface of sample in ageing procedure, which had great effects on the thermal stability and flame retardancy of the composites.     

MORPHOLOGY AND MECHANICAL PROPERTIES OF POLYPROPYLENE WITH in situ FORMED POLYAMIDE-6 FIBRILS

in situ Fibril formation of polyamide-6(PA6)in isotropic polypropylene(iPP)was first fabricated using a slit die extrusion and hot stretching process.Then the prepared materials were subjected to injection molding in the temperature range higher than the melting temperature of iPP but lower than that of PA6.The obtained injection-molded samples were characterized via scanning electron microscopy(SEM),differential scanning calorimetry(DSC)and two-dimensional wide- angle X-ray scattering(2D-WAXS).Mechanical properties were also investigated.The SEM result shows that the optimum fibril formation could be only achieved in the range of 20 wt% to 30 wt% of PA6 content for the studied system.The fibril morphology changes along the sample thickness in the injection-molded bars.The fibril morphology in the skin layer was better than that in the core layer.2D-WAXS results showed that the orientation of PP decreased with the increase of PA6 content,which indicated that the orientation of PP was confined by PA6 fibrils.Combined consideration of mechanical properties and morphology indicates that only PP/PA6 composites with 20 wt% of PA6 content show better properties because of the better fibril morphology and PP chain orientation.     

Analysis of fracture behaviour of fibre reinforced polypropylene using R-curve concept

Experimental results for investigation of dynamical crack resistance curves in the instrumented Charpy impact test on polypropylene (PP)/glass fibre composites are presented. For this purpose the multiple specimen R-curve method, stop-block technique is used. With the aid of J-integral versus stable crack growth (δa) curves the influence of a special coupler system on crack toughness as resistance against stable crack growth is discussed. It is shown that it is possible to quantify different energy dissipative processes with the new fracture mechanical material value J × T₇ (T₇ - tearing modulus). The problems of determining physical crack initiation values for short fibre composites are discussed. The physical material background for using the ‘plastic hinge’ model to describe the deformation behaviour of PP/glass fibre composites is shown, using the example of selected crack opening displacement (σ) versus δa curves.     

Investigations on the recycling of hemp and sisal fibre reinforced polypropylene composites

Microscopic, mechanical, rheological and thermal tests were carried out in order to determine the recycling behaviour of PP/vegetal fibre composites. Different composites using hemp and sisal were characterized. All results were compared with PP-g-MA/hemp composites and PP/glass fibre composites.The results prove that mechanical properties are well conserved with the reprocessing of PP/vegetal fibre composites but that there is poor adhesion between the fibres and PP without any treatment. The addition of PP-g-MA shows an improvement of the bonding evidenced by MEB pictures. Vegetal fibres induce an increase in the percentage of crystallinity χ_c and in the crystallization temperature T_c which can be explained by the nucleating ability of the fibres improving crystallization of PP. The Newtonian viscosity η₀ decreases with cycles, indicating a decrease in molecular weight and chain scissions induced by reprocessing. The decrease of fibre length with reprocessing could be another reason for viscosity decrease.     

Influence of an interfacial agent on the structure of polypropylene-polyamide fibres

In this paper the structure and properties of fibres prepared from the polypropylene/polyamide (PP/PA6) blend have been studied as a function of the interfacial-agent (IFA) content. For this purpose the grafted polypropylene-maleic anhydride copolymer was used. Fibres containing 20% of PA6 and 80% of PP possess the phase matrix-fibril structure. The size and distribution of fibres in the dispersed PA6 phase in the PP matrix depend on the interfacial-agent amount. Due to the indirect nucleating effect the PA6 phase has been found to act, in the presence of the interfacial agent, on the PP crystallization during fibre formation. As a result, undrawn fibres have the more pre-oriented and crystalline PP matrix with the morphological rod-like structure. The pre-orientation of the dispersed fibrilar PA6 phase is minimum. Mechanical properties of the drawn blended fibres are favourably influenced provided that the interfacial-agent concentration is higher than 1%. The growing rate of the mutual interaction between the components was mostly reflected in the increased values of Young's modulus.     

Accelerated weathering of unbleached and bleached Kraft wood fibre reinforced polypropylene composites

In this paper, combined moisture/ultraviolet (UV) weathering performance of unbleached and bleached Kraft wood fibre reinforced polypropylene (PP) composites was studied. Composites containing 40 wt% fibre with 3 wt% of a maleated polypropylene (MAPP) coupling agent were fabricated using extrusion followed by injection moulding. Composite mechanical properties were evaluated, before and after accelerated weathering for 1000 h, by tensile and impact testing. Differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were also carried out to assess the changes occurring during accelerated weathering. Bleached fibre composites initially showed higher tensile and impact strengths, as well as higher thermal stability and greater crystallinity. During accelerated weathering, both unbleached and bleached fibre composites reduced tensile strength (TS) and Young's modulus (YM), with the extent of the reduction found to be similar for both unbleached and bleached fibre composites. Evidence supported that the reduction of TS and YM was due to PP chain scission, degradation of lignin and reduced fibre-matrix interfacial bonding.     

Low velocity impact response of flax/polypropylene hybrid roving based woven fabric composites: Where does it stand with respect to GRPC?

Flax-PP based thermally bonded roving (TBR) has a unique structure where the flax fibres remain twist-free and fully aligned along the roving axis. The present study describes an experimental investigation on the low velocity impact (LVI) behaviour of the TBR based woven fabric composites and compares the same with plain woven glass fabric reinforced PP composites (GRPC). Two different fabric architectures namely plain woven (PW) and unidirectional (UD) are fabricated using flax/PP based TBR. These TBR based woven fabrics and the glass fabric/PP sheets are consolidated in a compression moulding machine and the resultant composite-laminates are tested for their LVI behaviour. The impact test results revealed that the glass/PP composites absorb more energy and exhibit a higher peak load than both TBR based PW and UD fabric composites. However, the specific load and energy of all flax/PP composites are higher than the glass/PP composite. The damage tolerance of all composite laminates are evaluated by comparing their flexural strength before and after the impact. It is observed that the proportionate loss in flexural strength due to impact thrust is larger in case of glass/PP composites than all flax-PP composites.     

Effect of Montmorillonite on the Crystallization,Rheological and Physical Behavior of Polyamide-6/Polylactic Acid Blends

Organic montmorillonite (OMMT)/polyamide-6 (PA6)/polylactic acid (PLA) composites were prepared via a step melt compounding process using a twin screw. The effect of OMMT content on the crystallization behavior, as well as rheological and mechanical properties of the composites was carried out by differential scanning calorimetry, differential mechanical analysis, and using an advanced rheometer and a material testing machine. The crystallization behavior of the polymers was studied using a dynamic rheology method, which allowed to determine the onset of nucleation and obtain semiquantitative data on the nucleation density. The results revealed that the interaction between the OMMT and the PA6/PLA inhibits the molecular chain segment motion, which reduces the nucleation temperature, the crystal growth temperature, the melting temperature and the glass transition temperature of the samples. However, the PA6/PLA/OMMT composites showed better mechanical properties than the PA6/PLA composites.     

Phase morphology development in PP/PA6 blends induced by a maleated thermoplastic elastomer

The effects of maleated thermoplastic elastomer (TPEg) on morphological development of polypropylene (PP)/polyamide 6 (PA6) blends with a fixed PA6 content (30 wt %) were investigated. For purpose of comparison, nonmaleated thermoplastic elastomer (TPE) was also added to the above binary blends. A comparative study of FTIR spectroscopy in above both ternary blends confirmed the formation of in situ graft copolymer in the PP/PA6/TPEg blend. Dynamic mechanical analysis (DMA) indicated that un‐like TPE, the incorporation of TPEg remarkably affected both intensity and position of loss peaks of blend components. Scanning electron microscopy (SEM) demonstrated that PP/PA6/TPE blends still exhibited poor interfacial adhesion between the dispersed phase and matrix. However, the use of TPEg induced a finer dispersion and promoted interfacial adhesion. Transmission electron microscopy (TEM) for PP/PA6/TPEg blends showed that a core‐shell structure consisting of PA6 particles encapsulated by an interlayer was formed in PP matrix. With the concentration of TPEg increasing, the dispersed core‐shell particles morphology was found to transform from discrete acorn‐type particles to agglomerate with increasing degree of encapsulation. The modified Harkin's equation was applied to illustrate the evolution of morphology with TPEg concentration. “Droplet‐sandwiched experiments” further confirmed the encapsulation morphology in PP/PA6/TPEg blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1050–1061, 2006     

马来酸酐接枝热塑性弹性体在PP/PA6共混物中的作用

研究了马来酸酐接枝热塑性弹性体 (TPEg )作为增容剂对聚丙烯 (PP) 尼龙 6 (PA6 )共混体系的相容性、相态以及物理力学性能的影响 .研究结果表明TPEg的加入大大改善了PP PA6共混体系的相容性 ,且随TPEg含量的增大分散相粒径明显降低 ,共混物的韧性以及延展性大大提高 ,同时拉伸强度及模量仍保持较好的水平 .TPEg增容的PP PA6共混物的非等温结晶行为的研究表明 ,共混物中PP和PA6的结晶行为不同于各自纯的聚合物 ,PA6作为成核剂使PP的结晶温度提高 ;而PA6由于TPEg的加入 ,出现分级结晶现象 ,一级结晶温度略低于纯PA6的结晶温度 ,且随TPEg含量增大结晶受阻 ,二级结晶温度与PP的接近 .由于PP、PA 6以及TPEg之间存在较强的相互作用 ,三元共混物中PP及PA6的玻璃化转变温度分别较其纯聚合物升高 .基于上述结果 ,提出了本共混体系的结构模型     

聚酰胺热氧化降解机理

通过详细分析测定反应产物 ,研究了聚酰胺 (PA6)的热氧化降解机理 .用化学方法测定了PA6热氧化过程中几种主要基团含量的变化 ,对PA6热氧化的气相挥发产物进行收集和分析鉴定 ,还对经过氧化的PA6样品进行水解并用GC MS法对水解产物进行了分析鉴定 .在这些实验结果的基础上 ,提出了较完整的聚酰胺热氧化降解机理 .该机理包含了自由基在与酰胺基的羰基相连的亚甲基上的夺氢反应及一系列自由基加成环化和诱导断链的反应 ,能很好地解释反应产物的分析结果 .     

Damping analysis of nonwoven natural fibre-reinforced polypropylene composites used in automotive interior parts

The aim of this work is to evaluate the dynamic properties of nonwoven flax, hemp, kenaf and glass fibre-reinforced polypropylene (PP) composites. Also, the influence of some parameters, such as the type of reinforcement, the fibre/matrix weight ratio, the fibre orientation and the porosity content, on the damping behaviour of these nonwoven composites is investigated. To this end, a free flexural vibrations analysis was conducted to experimentally identify their natural frequencies and their associated loss factors. The obtained results show that the nonwoven composites reinforced by natural fibres present higher loss factors compared with those of the glass-PP composite. These interesting damping properties make these nonwoven composites very attractive for automotive applications where the dissipation of vibrations is highly requested.     

Investigations on the interactions between Li-TFSI and glass fibers in the ternary PP/GF/Li-TFSI composites

The polypropylene/glass fiber(PP/GF) composites with excellent antistatic performance and improved mechanical properties have been reported by incorporation of a very small amount of the organic salt, lithium bis(trifluoromethanesulfonyl)imide(Li-TFSI), into the PP/GF composites. It was considered that GF could play the role as the pathways for the movements of ions in the ternary composites. In this work, the interactions between Li-TFSI and glass fiber and the effects of such interactions on the physical properties of the composites have been systematically investigated. Three types of glass fibers with different ―OH group concentrations have been prepared in order to compare the interactions between GF and Li-TFSI. It was found that the ―OH group concentrations on the surface of glass fiber have significant effects on interactions between glass fibers and Li-TFSI. Such interactions are crucial for both the antistatic and mechanical performances of the final PP/GF/Li-TFSI composites. The investigation indicated that the GF with high ―OH group concentrations confined the movement of TFSI-, which decreased the antistatic properties of PP/GF/Li-TFSI composites. On the other hand, the GF with low ―OH group concentrations inhibited the absorption of Li-TFSI onto the GF, which also hindered the formation of Li-TFSI conductive pathway. The best antistatic performance of the ternary composites can be achieved at the intermediate ―OH concentrations on the GF.     

碳纤维预浸料挥发分测试方法改进

碳纤维预浸料挥发分的测试对于复合材料的工艺成型和制品的使用性能至关重要。为了解决碳纤维预浸料挥发分测试数据偏离理论值的问题,根据基体类型的差异,对挥发分测试方法进行了改进。对烘焙温度和烘焙时间进行考察试验。通过试验确定4211体系预浸料烘焙温度为160℃,烘焙时间为20 min,;氰酸酯体系预浸料烘焙温度为180℃,烘焙时间为60 min,并且需在金属网的下面加入恒重的收集皿。测试方法改进后,测试结果与理论值接近,且测定结果的标准偏差从0.75下降至0.12,提高了挥发分测试结果的精密度和准确度。     

Effect of maleic anhydride-grafted ethylene-propylene rubber on the mechanical, rheological and morphological properties of organoclay reinforced polyamide 6/polypropylene nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic modified montmorillonite (organoclay) were compatibilized with maleic anhydride-grafted ethylene-propylene rubber (EPRgMA). The blends were melt compounded in twin screw extruder followed by injection molding. The mechanical properties of PA6/PP nanocomposites were studied by tensile and flexural tests. The microstructure of the nanocomposite were assessed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The dynamic mechanical properties of the PA6/PP blend-based nanocomposites were analyzed by using a dynamic mechanical thermal analyzer (DMTA). The rheological properties were conducted from plate/plate rheometry via dynamic frequency sweep scans. The melt viscosity in a high shear rate region was performed by using a capillary rheometer. The strength and stiffness of the PA6/PP-based nanocomposites were improved significantly with the incorporation of EPRgMA. Adding EPRgMA to the PA6/PP blends resulted in a finer dispersion of the PP phase. TEM and XRD results revealed that the organoclay was dispersed more homogeneously in the presence of EPRgMA, however, mostly in the PA6 phase of the blends. DMTA results showed that EPRgMA worked as an effective compatibilizer. The storage (G′) and loss moduli (G″) assessed by plate/plate rheometry of PA6/PP blends increased with the incorporation of EPRgMA and organoclay. Furthermore, the apparent shear viscosity of the PA6/PP blend increased significantly for the EPRgMA compatibilized PA6/PP/organoclay nanocomposite. This was traced to the formation of an interphase between PA6 and PP (via PA6-g-EPR) and effective intercalation/exfoliation of the organoclay.     

超细聚酰胺6粒子增韧聚丙烯体系的研究

采用磨盘形力化学反应器室温下制备了聚丙烯 (PP) /聚酰胺 6 (PA6 )超细粉体 ,研究了其粒度、粒度分布及PA6超细粒子填充对PP力学性能的影响 .结果表明 ,磨盘形力化学反应器可有效实现PP/PA6的粉碎 ,所得粉体平均粒径达微米级 ,初级粒子尺寸甚至可达纳米级 ,粒度分布呈双峰分布状态 .在PA6和PP熔点之间的温度下加工可制得PA6超细粒于填充的PP/PA6共混体系 ,其力学性能明显好于PP/PA6简单共混体系 ,30 %PA6用量下 ,拉伸强度由 2 3 .2MPa提高至 2 9 3MPa ,Izod缺口冲击强度由 4.6 2kJ/m2 提高到6 .34kJ/m2 .形貌分析结果表明 ,由于基本保持了PA6超细粉体的原始尺寸 ,填充体系中PA6相区尺寸小、分布均匀 ,与使用增容剂得到的相区结构类似 .